My '97 4.0L has 254,000 miles on her. Previous owner had it well maintained, always serviced regularly by a mechanic for 20 years. It runs like a clock. But I looked through all the old service records and the timing chain was never replaced.

I put a wrench on the crank bolt and, with the distro cap off, I watched the rotor. It seemed to me that I could move the crank bolt left and right maybe 1/8th or 1/16th of a turn before the rotor moved.

So it's probably stretched and for its age that is no surprise.

My question is: do I really need to replace it? I'll have to take apart the entire front end of the engine, in this order: radiator, fan, serpentine belt, power steering pump, water pump, alternator and bracket, harmonic balancer, font main seal. Right? So I'll need to rent a harmonic balancer removal tool and seal puller tool.

How much is all that worth the effort? The engine runs great but it's probably not as powerful and fuel efficient as it once was. Getting up to speed on the highway takes a while and I'm getting 14 mpg city and 18 mph highway (31" tires). So not bad but not great.

I do plan on having her for a while longer. Maybe take her all the way to the 300,000 mile club. I'm taking her on a very important overland trip this July, about 2,500 miles round trip, so she needs to be in tip top shape.

What do you think?

 

If the motor is "running great" and you are getting 18mpg with 31s on the highway your motor is probably doing just fine. The fine tuning of the timing is controlled by the computer on the Jeep, and as long as it is compensating for any stretch in the timing chain (which by your description, it is), I would not fix what is not broken.


If it was having any serious problems with timing, I think you would see much bigger symptoms. (In your case, it would seem you are not seeing any symptoms at all).


Has it always had 31" tires on it? If not, that is what is likely causing it to take a little more time to get up to speed, and causing slightly lower mpg's in the city. You may improve city driving efficiency a little by using 3rd instead of D. The XJ likes to shift into 4th (drive) pretty early, and on bigger tires at lower speeds (city driving) that is not great for gas mileage.

 

The computer can control the timing of the ignition and fuel injector pulses but it can't fix a retarted valve timing.

Yeah the slower highway speeds is probably due to the larger tires. Around town its fine though

So, another point that I can make, I checked the compression a few weeks ago and all cylinders were withing 140-150 psi. So if the valve timing is off such that the intake and exhaust valves are closing later in the stroke, then I would be loosing compression. But my compression is great! Therefore I'm going to conclude that I don't need to fix the timing chain! Yay!

 

I should say that I already have the timing gear set, ordered it from Rock Auto months ago, and yesterday I took the radiator out and got the engine in TDC. Should I just go for it? What can go wrong??

 

wasted effort. it will lunch a valvetrain component long before the timing chain. lifter, rocker, valve etc.

 

Wasted effort at best, major self-induced head ache at worst! That's what I'm starting to lean towards now.

If it's not broken don't fix it

I'm watching youtube vids right now and apparently just pressing the harmonic balance off and on is a big job with a lot of things that can go wrong, especially for a DIY guy like myself. A lot of special tools needed, that may or may not be avaible in my town; gotta remember to remove the special washer before pulling the balancer with the special tool; gotta torque it back to the right spec and I don't have a torque wrench; etc.

The little slack I felt when turning the crank bolt is not really telling of a problem. Even a brand new timing chain will have some slack. You actually don't want them overly tight because it can put strain on the cam bearings. They also don't really stretch too much unless they're improperly lubricated, but given the compression test I'd say my motor was pretty well taken care of.

Case closed! Put in the new radiator and be done! I can do that in less than an hour

 

It's not a Chevy or Ford.............

 

Seems to me that you want to dive in and do this. As an owner of two XJ's, I'd say go for it. You already have the radiator out and that is the hard part.. This will give you a chance to clean the whole front end for any future work. It's not that difficult to get the timing cover off. You will need a harmonic balancer puller. Once you get that off, you're all set. Clean everything and get the cover off and it's easy from there. This will give you more confidence to tackle other jobs that are inevitable on these Jeeps.
If you do this, be prepared with a new plastic piece that keeps the chain from slapping against the cover. It will be very brittle and may break when replacing it. You may want to consider the harmonic balancer too. I just had to replace the original on my 98. It will start sliding forward and will interfere with the fan. If you plan on keeping your XJ for a long time, this is pretty easy stuff and will make it good for another 100-200k miles.
If you have not replaced the water pump and thermostat, I'd do that at the same time. At the very least, this will give you peace of mind before you head on a 2500 mile trip.

 

I would do it, and change the harmonic balancer and timing chain seals at the same time.
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Not really that much effort if you already have the rad out. Shaves like 3 hours off (draining, removing, refilling and burping)

 

its been a few years since i did my radiator, but i remember it being like an hour job tops? Perhaps i'm just forgetting something hahahh

 

Hah I guess your right. Wasn't thinking when I said 3 hrs
Maybe a bit longer than an hour for me, but I'm slow and would probably flush everything at the same time

 

Did my 4.0 grand @200k. You will see an improvement. Pay close attention to the cam thrust bolt, the little spring, and the slug at the end make sure you get them back in right. Make sure the spring and slug are there. This keeps the cam from walking. in fact if possible, locate these and replace them. A torque wrench is your friend here for the bolts!! Also for the oil pan bolts. If you have the factory rubber oil pan gasket keep that do not cut it out in the front. Just torque the bolts and it won't leak. Recommend a napa chain set, they are built by cloyes and go on tight.
The balancer is a bit of a chore make sure you are well stocked on pullers of all types..the box stores never give you the right one. I rented 2 and still ended up using parts from both as well as a steering wheel puller and bolts.